Tosefta for Beitzah 72:2

[With respect to] water that has been exposed, we do not pour it into a public thoroughfare, we do not knead clay with it, we do not permit a Gentile to drink from it, nor the livestock of others, but [if one chooses,] one may give his own livestock to drink exposed water. One may not sprinkle it on his house, nor may he wash his face, his hands, or his feet with it. Others say, [the Sages] were only talking about an instance where he has scraped [his face, hands, or feet, and thus the presumptively poisoned water would penetrate his skin]. And how much water [is required to dilute the poison (Ter. 8:5)]? [For exposed water] on the ground, 40 seahs. Others say, 200 [seahs], whether dispersed or scattered. Rabbi Nechemiah says, enough to fill a swimmer's barrel (see Beitzah 36b:15).